How do weaponless male fiddler crabs avoid aggression?

The ecology and evolution of autotomy

Autotomy, the self-induced loss of a body part, occurs throughout Animalia. A lizard dropping its tail to escape predation is an iconic example, however, autotomy occurs in a diversity of other organisms. Octopuses can release their arms, crabs can drop their claws, and bugs can amputate their legs. The diversity of organisms that can autotomize body parts has led to a wealth of research and several taxonomically focused reviews. These reviews have played a crucial role in advancing our understanding of autotomy within their respective groups. However, because of their taxonomic focus, these reviews are constrained in their ability to enhance our understanding of autotomy. Here, we aim to synthesize research on the ecology and evolution of autotomy throughout Animalia, building a unified framework on which future studies can expand. We found that the ability to drop an appendage has evolved multiple times throughout Animalia and that once autotomy has evolved, selection appears to act on the removable appendage to increase the efficacy and/or efficiency of autotomy. This could explain why some autotomizable body parts are so elaborate (e.g. brightly coloured). We also show that there are multiple benefits, and variable costs, associated with autotomy. Given this variation, we generate an economic theory of autotomy (modified from the economic theory of escape) which makes predictions about when an individual should resort to autotomy. Finally, we show that the loss of an autotomizable appendage can have numerous consequences on population and community dynamics. By taking this broad taxonomic approach, we identified patterns of autotomy that transcend specific lineages and highlight clear directions for future research.

Do weaponless males of the hermit crab Pagurus minutus give up contests without escalation? Behavior of intruders that lack their major cheliped in male-male contests

In dyadic contests, theoretical studies have predicted that weaker contestants are less likely to engage in fights to minimize the cost of aggression. Since the major cheliped of decapod crustaceans is critically important as a weapon, contestants without a major cheliped should be more likely to give up the contests. We therefore examined whether loss of the major cheliped by the hermit crab Pagurus minutus would affect their decision to escalate male–male contests over guarded females. Intruders without a major cheliped showed no difference in the frequency of escalation compared with intact intruders, and the decision to give up was affected by the body size difference between the contestants. After escalation, compared with intact intruders, intruders without a major cheliped had significantly decreased success of takeover of a female from opponents, suggesting a strong disadvantage of losing their major cheliped. Although the decision of weaponless intruders to escalate seems irrational, several factors, such as poor accuracy of resource holding potential assessment, the influence of body size, and a high benefit to cost ratio of male–male contests, may have affected their behavior.

Alternative mating tactics and male mating success in two species of fiddler crab

The use of alternative male mating tactics can determine the strength of sexual selection on male traits and have implications for sexual dimorphism. We examined size-based mating success in two species of fiddler crabs where males use each of two alternative tactics to obtain matings. InUca annulipes, larger males were more successful when using the primary mating tactic (burrow mating) but the full size range of males mated when using the secondary tactic (surface mating). InUca urvillei, both burrow and surface mating males were larger than the average sized male in the population. Standardised directional selection gradients indicated that selection on male size was stronger inU. urvilleithanU. annulipes, reflecting the differences between species in male mating success. Our results also showed that sexual size dimorphism was greater in the species with stronger sexual selection on male size than in the species with weaker sexual selection.

The evolutionary ecology of deception

Through dishonest signals or actions, individuals often misinform others to their own benefit. We review recent literature to explore the evolutionary and ecological conditions for deception to be more likely to evolve and be maintained. We identify four conditions: (1) high misinformation potential through perceptual constraints of perceiver; (2) costs and benefits of responding to deception; (3) asymmetric power relationships between individuals and (4) exploitation of common goods. We discuss behavioural and physiological mechanisms that form a deception continuum from secrecy to overt signals. Deceptive tactics usually succeed by being rare and are often evolving under co-evolutionary arms races, sometimes leading to the evolution of polymorphism. The degree of deception can also vary depending on the environmental conditions. Finally, we suggest a conceptual framework for studying deception and highlight important questions for future studies.